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Nuchal translucency is an exam, performed during ultrasound, which serves to measure the amount of fluid in the region of the neck of the fetus and which must be performed between the 11th and 14th weeks of gestation. This test is used to calculate the risk of the baby having a malformation or syndrome, such as Down syndrome.
When malformations or genetic diseases are present, the fetus tends to accumulate fluid in the nape of the neck, so if the measure of nuchal translucency is increased, above 2.5 mm, it means that there may be some change in its development.
What is the exam for
The nuchal translucency measurement does not confirm that the baby has a genetic disease or malformation, but it does indicate whether or not the baby has an increased risk of having these changes.
If the test value is changed, the obstetrician will request other tests such as amniocentesis, for example, to confirm or not the diagnosis.
How it is done and reference values
The nuchal translucency is done during one of the prenatal ultrasounds and, at this moment, the doctor measures the size and the amount of liquid that is in the region behind the baby's neck, without the need for any other special procedure.
The nuchal translucency values can be:
- Normal: less than 2.5 mm
- Altered: 2.5 mm or more
An examination with increased value does not guarantee that the baby suffers from any alteration, but it does indicate that there is a greater risk and, therefore, the obstetrician will request other tests, such as amniocentesis, which collects samples of the amniotic fluid, or cordocentesis, which evaluates a umbilical cord blood sample.Learn more about how amniocentesis or cordocentesis are made.
If during the ultrasonography the absence of the nasal bone is also verified, the risk of some malformation increases more, because the nasal bone is generally absent in cases of syndromes.
In addition to nuchal translucency, the mother's age and family history of chromosomal changes or genetic diseases are also important to calculate the baby's risk of having one of these changes.
When to do nuchal translucency
This examination should be done between the 11th to the 14th week of gestation, as it is when the fetus is between 45 and 84 mm in length and it is possible to calculate the nuchal translucency measurement.
It can also be known with morphological ultrasound of the first trimester, because, in addition to the measurement of the baby's neck, it also helps to identify malformations in the bones, heart and blood vessels.
Learn about the other tests that are needed in the first trimester of pregnancy.